017
FXUS63 KARX 161052
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
552 AM CDT Wed Sep 16 2026

.KEY MESSAGES...

- Shower and storm chances (30-50%) return tonight into Thursday
  morning with minimal impacts expected.

- There is increasing confidence in heavy rainfall on Friday
  into Saturday across the entire area with potential rainfall
  amounts of 1-3 inches with locally higher amounts possible.
  Flooding and river rises may occur where the heaviest rainfall
  amounts occur.

&&

.DISCUSSION...
Issued at 139 AM CDT Wed Sep 16 2026

Rainfall Potential Overnight Into Thursday Morning:

Passing low level anticyclonic flow evident on area VWPs has ushered
in a cooler, drier airmass over the forecast area compared to
previous few days with the recent frontal boundary shunted just
south into central Iowa. The anticyclonic flow center traverses east
of the forecast area through today, ushering in return flow and the
aforementioned frontal boundary with accompanying increased moisture
into tonight. Associated precipitation chances increase locally
tonight as mid level shear vorticity lobe and transient ageostrophic
ascent within the equatorward entrance region of a passing upper
level jet streak causing meager cyclogenesis. Overall impacts
appear minimal given diurnal timing abstaining more unstable airmass
upstream of the forecast area into central Minnesota.

Heavy Rain Friday Into Saturday:

Subsequent cyclogenesis of a Rocky Mountain Low through the Northern
Plains through Thursday returns heavy rain potential across the
Upper Mississippi River Valley initially Friday morning. Band of
strong low level frontogenesis collocated with 1.5"-2"+ PWATs results
in heavy rain probabilities quickly increasing through Friday
shifting east into Friday night. Strengthening of the low through
Friday night persists heavier rain potential into Saturday morning
across the forecast area. LREF (15.12Z) probabilities quickly
increase through Friday into Friday night with 40%/70% for 2" of
rainfall in 24 hrs in the GEFS/EPS. While overall placement may vary
some, the area of higher rainfall (2"+) values is quite widespread.
Resultant increased concerns for river flood primarily from west-
central (Black River) into central (Yellow River) and southwest
Wisconsin (Kickapoo River). As the flashiest of these rivers,
highest impacts would be along the Kickapoo River should this
solution come to fruition. While the combination of lagged
initialization (GEFS) with 72 hour forecast window limits
accompanying river flooding probabilities (HEFS), GEFS rainfall
probabilities remain lower than EPS/GEPS, increasing flooding impact
concerns and probabilities above current values.

Early Next Week: Staying Cooler Than Normal, Additional Rain Chances

As the rainfall from Friday and Saturday departs the local area,
northeasterly flow around the surface low will likely keep
temperatures slightly below normal into Sunday with median high
temperatures in the NBM hovering in the middle 60s to near 70. The
main point of forecast uncertainty as we head into next week will be
revolving around a potential cut-off upper-level low which guidance
has substantial disagreements on how to handle at this point in the
forecast cycle. Consequently, the NBM maintains some low-end
precipitation probabilities (15-40%) at this point from Sunday
through Monday which seems reasonable given the wide range of
solutions with this system. However, given the presence of this low
in the region into early next week, thinking that below normal
temperatures will maintain with median high temperatures in the NBM
hovering in the upper 60s to around 70 degrees.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 548 AM CDT Wed Sep 16 2026

VFR conditions are likely for the first half of this TAF cycle.
Light east wind and increasing high level clouds are expected
through the daytime hours. Confidence for rain showers leading
to lower visibility and low clouds developing has increased
after 00z. Rain showers should be relatively light with
reductions down to MVFR visibility possible at times. Low clouds
will continue to build in even after rain has ended which should
lead to MVFR/IFR ceilings to end this 24 hour period. In
addition to the low clouds, fog may also develop but confidence
in that scenario panning out is not high at this time.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.

&&

$$

DISCUSSION...Naylor/JAR
AVIATION...Muscha